1. Field of the Invention
The present invention is related to the field of fermentation, and more specifically to the production of L-amino acids via the fermentation of microorganisms.
2. Brief Description of the Related Art
L-Amino acids are industrially produced by fermentation using microorganisms belonging to the genus Brevibacterium, Corynebacterium, Escherichia, or the like. In such production methods, strains are used which are isolated from nature, or artificial variants of such strains. Furthermore, microorganism strains can be used which are modified by a recombinant DNA technique to increase activity of a basic L-amino acid biosynthesis enzyme, and so forth (EP 0643135 B, EP 0733712 B, EP 1477565 A, EP 0796912 A, EP 0837134 A, WO01/53459, EP 1170376 A, WO2005/010175, and WO96/17930).
When amino acids are produced using microorganisms, sugars are generally used as a main component of substrate, but glycerol can also be used as a substrate (EP 1715055 A and EP 1715056 A).
It is known that Escherichia coli has a plurality of genes which participate in glycerol metabolism. However, it has been revealed that, since a mutant strain deficient in glpK, which is a gene coding for glycerol kinase, or glpD, which is a gene coding for glycerol-3-phosphate dehydrogenase, cannot grow in a medium when glycerol is the sole carbon source, the major glycerol assimilation pathway of E. coli consists of glycerol kinase and glycerol-3-phosphate dehydrogenase (J. Bacteriol., 23 (2006) 8259-8271).
It is known that glycerol dehydrogenase of E. coli is also one of the enzymes which participate in glycerol metabolism, and it recovers a mutant strain deficient in the three genes of glpK, glpD and glpR, which is a gene of repressor of the glp regulon, from lethality thereof in a medium containing glycerol as a sole carbon source in screening using that strain (J. Bacteriol., 131 (1977) 1026-1028).
The pathway via glycerol-3-phosphate including glycerol kinase and glycerol-3-phosphate dehydrogenase is thought to be the main glycerol assimilation pathway of microorganisms belonging to the family Enterobacteriaceae as described above, and the glycerol assimilation pathway via dihydroxyacetone is an unnecessary pathway for glycerol assimilation of microorganisms belonging to the family Enterobacteriaceae.